TETRADYNAMIA. SILICULOSA^ 6S 



ers small and yellowish; silique eUiptic-oblong*, pubescent. 

 Flowering in May. On the gravelly hills of the Missouri, 

 from the river Platte to Fort Mandan, rare. 6. i?icang. 

 7 . Arabis. 

 Almost exclusively an European genus. 



452. ALYSSUM. L, (Gold of Pleasure.) 



Filaments of 2 of the stamina often internal- 

 ly toothed near the base. Silidt 2-celled, en- 

 tire, acuminated with the style, mostly pubes- 

 cent, subelliptic or globose. 



An obscurely defined genus. Most of the species as 

 in Arabis are furnished with a divided or stellate pubes- 

 cence; stems suffi'uticose as well as herbaceous; leaves 

 generally entire, flowers often yellow, the species with 

 this colour are said to be those only which produce the 

 denticulated filaments, (an American species with yel- 

 low flowers, and inflated globose pods, is totally desti- 

 tute of this distinction and yet unquestionably an Alys- 

 sum.) 



Species. 1. A. * dentatum. Stem erect, and herba- 

 ceous, recemes paniculate, axillary; radical leaves subrun- 

 cinately tootiied, and somewhat asperate, cauline linear- 

 lanceolate, sessile, nearly smooth, and partly entire; silicle 

 elliptic, compi-essed, pubescent and contorted, termina- 

 ted by a style nearly its length; peduncle longer than the 

 silicle. Draba Arabisans, Ph. not of Michaux? A plant so 

 distinct, could scarcely bear comparison with Draba inca- 

 na. Obs. Perennial or nearly so; (I have before me speci- 

 mens clothed with the vestigia of 3 years.) Pubescence 

 thin and not communicating any thing of a hoary appear- 

 ance so common in this genus, hairs with only 4 rays, or 

 decussated at right angles. Leaves all lanceolate and acute, 

 those of the stem remote. Seeds brown, elliptic, and 

 compressed, scarcely margined. Flowers not seen. Hab. 

 On the shelvings of slate" rocks; near Harper's Ferry in 

 Virginia, v. s. In Herb. Muhl. 



2. *ludoviciamim. Herbaceous and spreading; argente- 

 ously tomentose; svems numerous, simple, angular; leaves 

 linearly spathulate, entire, obtuse, attenuated; silicles el- 

 liptic, inflated, pubescent. Mijagrtim argenterim. Ph. 2. p. 

 434. Hab. On the high hills of the Missouri, and on the 

 shelvmgs of rocks. Flowering in April and May. Obs. 6 to 

 8 inches high. Perennial. ' Calix oblong, erect. Petals 

 obovate, entire, golden yellow. Filaments simple. Pedun- 

 cles about an inch long. Silicle tomentose, 2-valved, 2-cel- 



